Diabetes is the most common cause of ESRD in Western countries. This article describes the impact of glycemic control in the various stages of the disease and considers the impact of tight glycemic control on the development and progression of diabetic nephropathy (DN). The Diabetes Control and Complications Trial and the United Kingdom Prospective Diabetic Study have demonstrated in type 1 and type 2 diabetes that intensive glycemic control significantly reduces the risk for development of microalbuminuria. Although observational studies suggest an impact of glycemia also on the progression of DN, fewer data are available on the impact of improved metabolic control in secondary prevention. The long-term follow-up of the patients who participated in the Diabetes Control and Complications Trial (Epidemiology of Diabetes Interventions and Complications Study) demonstrated a sustained effect of previous tight glycemic control on both development and progression of DN. Finally, long-term normoglycemia, achieved by pancreas transplantation, is able not only to prevent the development of early diabetic glomerulopathy in kidney transplant recipients but also to halt progression and induce regression of the established diabetic renal lesions in nonuremic patients. Taken together, these studies strongly demonstrate that improvement in glucose control is the most important therapeutic approach in primary prevention. Tight glycemic control also is important in slowing progression of DN, and if blood glucose is normalized, then regression of DN can be achieved. Therefore, a target of glycated hemoglobin levels <7% should be recommended in all patients with diabetes.